A COSMIC SEARCHLIGHT

Streaming out from the center of the
galaxy M87 like a cosmic searchlight is one of nature's
most amazing phenomena, a black-hole powered jet
of electrons and other sub-atomic particles traveling
at nearly the speed of light. In this NASA Hubble
Space Telescope image, the blue of the jet contrasts
with the yellow glow from the combined light of
billions of unseen stars and the yellow, point-like
globular clusters that make up this galaxy.

At first glance, M87 (also known
as NGC 4486) appears to be an ordinary giant elliptical
galaxy; one of many ellipticals in the nearby Virgo
cluster of galaxies. However, as early as 1918,
astronomer H.D. Curtis noted a "curious straight
ray" protruding from M87. In the 1950s when the
field of radio was blossoming, one of the brightest
radio sources in the sky, Virgo A, was discovered
to be associated with M87 and its jet.

After decades of study, prompted by
these discoveries, the source of this incredible
amount of energy powering the jet has become clear.
Lying at the center of M87 is a supermassive black
hole, which has swallowed up a mass equivalent to
2 billion times the mass of our Sun. The jet originates
in the disk of superheated gas swirling around this
black hole and is propelled and concentrated by
the intense, twisted magnetic fields trapped within
this plasma. The light that we see (and the radio
emission) is produced by electrons twisting along
magnetic field lines in the jet, a process known
as synchrotron radiation, which gives the jet its
bluish tint.

M87 is one of the nearest and is the
most well-studied extragalactic jet, but many others
exist. Wherever a massive black hole is feeding
on a particularly rich diet of disrupted stars,
gas, and dust, the conditions are right for the
formation of a jet. Interestingly, a similar phenomenon
occurs around young stars, though at much smaller
scales and energies.

At a distance of 50 million light-years,
M87 is too distant for Hubble to discern individual
stars. The dozens of star-like points swarming about
M87 are, instead, themselves clusters of hundreds
of thousands of stars each. An estimated 15,000
globular clusters formed very early in the history
of this galaxy and are older than the second generation
of stars, which huddle closer to the center of the
galaxy.

The data were collected with Hubble's
Wide Field Planetary Camera 2 in 1998 by J.A. Biretta,
W.B. Sparks, F.D. Macchetto, and E.S. Perlman (STScI).
The Hubble Heritage team combined these exposures
of ultraviolet, blue, green, and infrared light
in order to create this color image.